A glow plug includes a ceramic structure that includes a ceramic substrate, a conductor layer disposed on a surface of the ceramic substrate, and a brazing filler material covering the surface of the conductor layer. The glow plug further includes a metal holding member that is electrically connected to the conductor layer through the brazing filler material and holds the ceramic structure. The glow plug including such a ceramic structure is used for assisting ignition of, for example, a diesel engine. The glow plug is required to have high heat resistance and high durability in order to correspond to increasingly strict environmental regulation (for example, see PTL 1).
However, in ceramic structures constituting conventional glow plugs, operation for a long time could cause a gap in a boundary between the ceramic substrate and the conductor layer. Consequently, when a glow plug including such a ceramic structure is attached to a desired position such as a cylinder, leakage could occur to decrease the air tightness.
The present invention was made in view of the circumstances described above, and it is an object of the invention to provide a ceramic structure, a ceramic heater, and a glow plug including the ceramic heater that are prevented from causing a gap in a boundary between a ceramic substrate and a conductor layer.